It is right to revive Frank McGuinness's iconic Irish play from 1985: it is both an astonishing feat of imagination by a Donegal Catholic and part of Hampstead's own 50-year history. But, while it is good to introduce the play to a new generation, I also became aware of what McGuinness omits to say and of his sometimes excessive emphasis on an apparent Ulster death-wish.

The form of the play is certainly original. It follows the progress of eight men from the 36th Ulster Division who brought to the battlefields of France their own baggage. Seen through the memory of the sole survivor, a guilt-ridden product of the Protestant Ascendancy named Pyper, it also shows how in war the men instinctively bond. The gay, upper-class Pyper falls in love with a young blacksmith. Two men from Coleraine help each other overcome their mutual fear, two Belfast boys brandish their tribal, anti-Fenian loyalty and a self-doubting priest finds consolation in the company of a secular sportsman. War, McGuinness suggests, unites men and extinguishes them.

The best scenes in the play remain as powerful as ever. The elder Pyper's opening monologue has a Beckettian severity. An episode of home leave articulates the mixed motives that drive the men on: sex, religion, patriotism, even guilt over Belfast's role in the Titanic disaster. And the high point, as always, remains the pre-battle moment when the men re-enact of the Battle of the Boyne by squatting on each other's shoulders and showing King Billy confronting King James; and when the Orange monarch stumbles, it is seen as a token of impending death.

But while McGuinness plausibly shows the present invaded by the past, he never acknowledges that the tragedy of the Somme, which produced 60,000 British casualties on the first day alone, was ultimately caused by Sir Douglas Haig's fatal tactics. And, while McGuinness can hardly be blamed for not foreseeing the Northern Irish peace process, his insistence on Ulster's doomed isolation and built-in sectarianism never admits the possibility of change.

Time has altered our perspective. But John Dove's production is impressively staged and acted. Richard Dormer as the half-mad younger Pyper and James Hayes as his older, embittered self are outstanding. Billy Carter also seethes with rage and anxiety as the priest torn between service to God and his king and Eugene O'Hare is touching as the blacksmith drawn to the self-hating Pyper. I found myself admiring McGuinness's skill in exploring the Protestant ethos while feeling the play tells only part of the story.